Without question, the advent of the personal computer revolutionized enterprise computing during the 1980s, quickly distributing processing power throughout an enterprise. As the personal computer distributed processing power, though, it also tended to distribute critical data throughout the enterprise. The enterprise world soon realized that such unfettered data distribution was difficult to manage. Critical data often was lost as individual computers failed, and just as often, the same data maintained in separate computers was inconsistent or unsynchronized.
The evolution of the two-tier “client/server” architecture resolved some of this tension between the benefits of distributed processing and the detriments of distributed data. In a two-tier enterprise information system (EIS), a server tier stores and manages enterprise data, while a client tier provides a user interface to the data in the server tier, as illustrated in FIG. 1. A conventional client tier also is responsible for implementing most of the business logic or data processing. In general, a client and a server rely on a request/response model for communicating with each other, in which the client sends a request (for data or other resources) to a server, and the server responds to the client. Note that, in this context, the terms “client” and “server” refer to the hardware and software, collectively, that implement each tier's respective functions. The client, though, generally is a distinct physical entity that is remotely connected to the server through a network. FIG. 1 depicts a classic embodiment of the two-tier architecture, in which a client provides the user interface and business logic, and a database server maintains the enterprise data and processes a client's request to retrieve or update the data. More particularly, two-tier client/server architecture 100 has a server tier in the form of server 120 that stores and manages enterprise data stored in database 122. A client tier in the form of client 110 provides user interface 114 for viewing and manipulating data maintained by server 120. Client 110 is also responsible for implementing most of the business logic 112 required for data processing. Server 120 processes request 130 to retrieve or update the data in database 122 and sends response 140 to client 110.
Probably the most prolific example, though, of a tiered, client/server architecture is the World Wide Web (“the web”). Originally, the web comprised only two tiers—web servers and web clients (more commonly known as web “browsers”). FIG. 2 depicts the original web architecture, which is almost identical to the classic database architecture depicted in FIG. 1. In this case, however, user interface 114 is replaced by a web browser 116 and database 122 is replaced by web pages 124. Early incarnations of server 120 merely provided access to static web pages 124 by retrieving them and sending them over the network to the client 110, and the client 110 did nothing more than request and display them. Generally, though, web browser 116 may request any type of web resource that is available to server 120. Every web resource is associated with a Uniform Resource Indicator (URI), which uniquely identifies the resource. More particularly, web page's 124 URI identifies the location of server's 120 host, and the name and location of web page 124 within server's 120 file system. Consequently, web page's 124 URI is also known as a Uniform Resource Locator (URL). For example, the URL of a hypothetical web page 124 named “bar.html” in the “foo/” directory of web server 120 named “example.com” would be “example.com/foo/bar.html.” Web browser 116 and the web server 120 adhere to the HyperText Transfer Protocol (HTTP), a standard network communication protocol, in order to exchange requests and responses over the network. Thus, the complete URI for the hypothetical “bar.html” web page 124 would be http://example.com/foo/bar.html.
Although the two-tier architecture has enjoyed much success over the years, sophisticated multi-tier client/server systems slowly have displaced this traditional model. As FIG. 3 illustrates, a multi-tier system such as multi-tier system 300 places at least one intermediate (or “middleware”) component between client 110 and server 120. Generalized “n-tier” systems include n layers of software that provide a different layer of services at varying levels of detail to the layers above and beneath them, where n is any number. While client 110 tier generally retains its traditional responsibility for implementing user interface 114, one or more middle tiers implement business logic 112. A middleware component that implements business logic 112, as depicted in FIG. 3, commonly is referred to as an “application server.” Additional tiers usually implement the traditional server 120 tier functions, which include data management and retrieval.
Web server technology continued to evolve as well, and eventually embraced techniques for dynamically generating web pages. These techniques allowed a web server to access enterprise data, usually through a database server, and to process the data before responding to a client's request, as FIG. 4 illustrates.
Clearly, there is some functional overlap between clients, web servers, application servers, and database servers, with each component exhibiting unique advantages. In particular, ubiquitous web browsers such as MOZILLA, NETSCAPE, and INTERNET EXPLORER provide inexpensive (if not free), cross-platform user interfaces that comply (usually) with standard formats (e.g. HTML) and protocols (e.g. HTTP). Similarly, web servers generally offer a cross-platform, standard-compliant means of communicating with the browsers; application servers provide cross-platform access to customized business logic; and database servers provide cross-platform access to enterprise data. Today, an EIS generally integrates each of these components, thus capturing the best of all worlds and providing an architecture for implementing distributed, cross-platform enterprise applications. FIG. 5 depicts one embodiment of a modem EIS, in which distributed, cross-platform web architecture 500 combines web server 180, application server 150, and server 120 to provide cross-platform access to customized business logic 112 and enterprise data stored in database 122.
Although the modem EIS provides an architecture for implementing distributed, cross-platform enterprise applications, historically, each EIS component has not been portable to other platforms (i.e. platform independent). In 1995, however, Sun Microsystems, Inc. (“SUN”) introduced a new product, “JAVA,” that provided the foundation for building such portable components. As introduced in 1995, JAVA comprised an object-oriented programming language and a processing architecture (the “JAVA virtual machine” or “JVM”). See David Flanagan, Java in a Nutshell 3 (3d ed. 1999). SUN touted JAVA as the only “write once, run anywhere” development tool, meaning that a developer could create a JAVA application and run it on any platform. Id. at 6. More accurately, though, JAVA allows a developer to create a JAVA application and run it on any platform having a JVM. Id. Several years later, SUN released a new JAVA specification, which included new language features and a new library of JAVA classes (the “JAVA platform”) designed to support stand-alone application development. See James McGovern et al., Java 2 Enterprise Edition 1.4 Bible 5 (Wiley Publishing, Inc. 2003). SUN marketed this specification as JAVA 2 Standard Edition (J2SE). Id. Finally, in 1998, SUN released JAVA 2 Enterprise Edition (J2EE), which addressed the need for developing and deploying portable enterprise applications. Id. J2EE defines a standard multi-tier architecture for an EIS. Id. J2EE comprises a specification that defines the logical application components within an EIS, and defines the roles played in the development process. Id. All J2EE components run within a “container” program, which the J2EE specification also defines. Id. at 6. The components of a J2EE platform include application clients, applets, web components, and server components. Id.
A JAVA “servlet” is a type of J2EE web component that can perform the application processing assigned to a middle tier, act as a proxy for a client, and even augment the features of the middle tier by adding support for new protocols or other features. See generally MageLang Inst., The Java Servlet API, at http://java.sun.com/developer/onlineTraining/Servlets/Fundamentals/servlets.html (last visited Aug. 18, 2004). A servlet also can extend a web or application server's functionality and support dynamic generation of HTML documents. In this respect, a JAVA servlet is similar to native web server extension technologies such as Microsoft's ISAPI and ASP and Netscape's NSAPI. See, e.g., Clifford J. Berg, Advanced Java 2 Development for Enterprise Applications 604 (2d ed. 1999).
Like all J2EE components, a servlet runs within a container (sometimes also referred to as a servlet “engine”), which manages the servlet. The container loads and initializes the servlet, passes requests to the servlet and responses to a client, manages multiple instances of a servlet, and acts as a request dispatcher. The container also is responsible for destroying and unloading the servlet. For example, if the servlet's resources are needed elsewhere, the container destroys and unloads the servlet and then subsequently reloads and reinitializes the servlet if it is requested again. A servlet also is destroyed at the end of its useful life, and when the container shuts down. See Jeanne Murray, Building Java HTTP Servlets (September 2000), at https://www6.software.ibm.com/developerworks/education/j-servlets/j-servlets-ltr.-pdf (last visited Aug. 18, 2004). A container passes initialization information to a newly created servlet through a ServletConfig object. See, e.g., MageLang Inst., supra. While running, a servlet can get information about its environment (or “context”) through a ServletContext object. Id.
In practice, a client sends a request to a server, which specifies a servlet's URI. The server, or more likely, a container running within the server, then creates an instance (“instantiates”) of the servlet identified by the URI. The server or container also creates a thread for the servlet process. The servlet instance then stays active until the container explicitly destroys the servlet or the server shuts down. The container sends the request to the servlet, which processes the request and builds a response. The servlet dynamically constructs a response using information in the client request, and, if necessary, data from other EIS components. If the request uses HTTP, the servlet wraps the response in HTML. Finally, the servlet passes the response back to the client, through the container. Murray, supra.
Naturally, SUN provides a JAVA Servlet Application Programming Interface (API), which defines a standard interface between a client, container, and servlet. See, e.g., id. The JAVA Servlet API includes two packages, one that supports generic protocol-independent servlets (the “javax.servlet” package), and one that provides specific support for HTTP (the “javax.servlet.http” package). Id. Thus, a generic servlet must implement the javax.servlet.Servlet interface. Such generic servlets typically implement this interface by extending the javax.servlet.GenericServlet class, which is implemented in the javax.servlet package. A servlet that needs HTTP support (a “web servlet”), on the other hand, should extend the javax.servlet.http.HttpServlet class, which is implemented in the javax.servlet.http package. Almost all servlets written today are designed to use the HTTP protocol, so most servlets currently extend the javax.servlet.http.HttpServlet class. See Mark Andrews, Story of a Servlet: An Instant Tutorial, at http://java.sun.com/products/servlet/articles/tutorial/ (last visited Aug. 18, 2004).
The Servlet API generally provides support in four categories: (1) servlet life cycle management; (2) access to servlet context; (3) utility classes; and (4) HTTP-specific support classes. See, e.g., MageLang Inst., supra. A servlet and container communicate through the API methods, which include init(ServletConfig), and service(ServletRequest, ServletResponse). Id.
As noted above, a container instantiates and initializes a servlet the first time it is needed. To initialize the servlet, the container invokes the servlet's init( ) method, passing a ServletConfig object as an argument. The ServletConfig object includes a getServletContext( ) method that returns a ServletContext object, which represents the server's environment. Id. Generally, the init( ) method opens database or other server connections required to service a request. See, e.g., Murray, supra.
The service( ) method is the “heart” of the servlet. MageLang Inst., supra. A container invokes the service (ServletRequest, ServletResponse) method whenever a request invokes the servlet. Thus, each request message from a client results in a single call to the servlet's service( ) method. The service( ) method reads the request and produces the response message from its two parameters: a ServletRequest object, and a ServletResponse object. A ServletRequest object consists of name/value pairs of parameters and an InputStream. A ServletResponse object represents the servlet's reply back to the client. Id.
The Java Servlet API is a standard supported by many web servers, especially those that are bundled with application servers. Berg, supra, at 604. Thus, the Servlet API provides a very convenient and secure framework for creating distributed applications that can serve dynamically generated HTML, and also can access other network servers, such as databases and application servers. Id. Of course, to implement a distributed application with Java servlets, a web server must run a servlet container or an application server that has a servlet container capable of supporting the life cycle of servlets. McGovern et al., supra, at 78. A servlet container running within a web server is referred to generally as a “web container.” Likewise, a distributed application that relies on web servlets is referred to generally as a “web application.” Because web servlets plug into an existing server, they leverage a lot of existing code and technology. The server handles the network connections, protocol negotiation, class loading, and more. MageLang Inst., supra.
A JavaServer Page (JSP) is another type of J2EE web component that supports dynamic HTML generation. See, e.g., McGovern et al., supra, at 113. A JSP, in form, is similar to a static HTML document that contains embedded Java code. Id. at 7. Functionally, though, a JSP is nothing but a servlet that a container automatically generates from a file containing valid HTML and JSP tags. Id. at 115. The container interprets the JAVA code and incorporates any output that the code generates into the HTML content before returning the content to a client. Berg, supra, at 631. In practice, most JSP implementations compile portions of a JSP page into one or more runtime objects that can be cached for improved efficiency. Id.
Servlets have become an important adjunct to application servers by providing a web-traversable gateway. Many products extend application server features including security, transaction management, and load balancing to the servlet container, thereby allowing servlets to become the universal gateway to these services. Berg, supra, at 607. A “gateway” servlet, found in application servers such as Tomcat and JBoss, handle specific Uniform Resource Locator (URL) patterns and route requests for those URLs to their final destination (typically a client) after reading configuration information and initializing the target.
A gateway servlet, though, like all J2EE components, must run within a container. The container loads and initializes the servlet, passes requests to the servlet and responses to a client, manages multiple instances of a servlet, and acts as a request dispatcher. The container also destroys the servlet at the end of its useful life. Servlets are unloaded and removed from memory when the container shuts down. Consequently, the container may remove a gateway servlet at any time, which may decrease application performance and/or impose additional requirements in container design. Gateway servlets also must undergo the lifecycle of a servlet, which may adversely affect application performance as well. Moreover, the gateway servlet concept does not provide a convenient means for implementing a downstream container that can leverage any of the host container's optimizations.
While the above-described gateway servlets fulfill their respective, particular objectives and requirements, the aforementioned prior art does not describe an extensible URI-pattern-based servlet request-processing framework that allows processing and responding to requests for resources sent over a network by client programs to application programs in an EIS. The prior art makes no provision for providing gateway servlet functionality without being subjected to the constraints of traditional servlet design. Thus, there is a need in the art for an improved means of processing URI requests that overcomes the disadvantages of the current gateway servlet technology but still allows a developer to extend and customize a web application's functionality. Such an improved means also should reduce the execution path of any given request and handle most standard lifecycle events (such as J2EE security calls and class loading) and web container specific events. In this regard, the present invention substantially fulfills this need. In this respect, the extensible URI-pattern-based servlet request processing framework according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in doing so provides an apparatus primarily developed for the purpose of processing and responding to requests for resources sent over a network by client programs to application programs in a multi-tiered data processing system.